example, cooking and cleaning the bathroom are level 3, washing the family ’ s clothes is level 2, and sweeping is level 1. We then combined the coding of the mother ’ s reports on each childtodeveloptwoscalesthatsummarizethesiblingpair ’ scol-laborative initiative and adult control of their household work. (The two siblings had similar reports of collaborative initiative and adult control.) The children ’ s collaborative initiative scale took into ac-count the range and complexity of their voluntary contributions, to distinguish pitching in to perform minimal vs. very responsible work. It ranged from 0 (minimal work with no initiative, just adult control) to 8 (regularly voluntarily carrying out complex household work without adult control). The adult control scale ranged from 0 (no adult control) to 2 (work done with adult control and no collaborative initiative). The scales are detailed in SI Appendix . Primary coding was done by L.A. and A.L.F. For reliability, a bilingual assistant blind to the hypotheses coded one-third of the data. Reliability between the blind coder and the other two coders was excellent for both scales ( r = 0.93 and k = 0.80). Results: Relation Between Ways of Engaging at Home and in the Planning Task. Background analyses of cultural differences in ways of contributing at home fit the pattern found in refs. 38 and 39. Mexican-heritage sibling pairs were reported to collaborate with initiative at home more regularly than middle-class Euro-pean American pairs ( M s = 4.63 vs. 1.18, respectively, on our 0 – 8 scale; SDs = 2.7 and 1.7, respectively), t (37) = 4.44, P < 0.001. Middle-class European American pairs were reported to con-tribute to household work based on adult control more than Mexican-heritage siblings ( M s = 1.65 and 0.73, respectively, on our 0 – 2 scale; SDs = 0.59 and 0.73, respectively), t (37) = 4.00, P < 0.001. The two Mexican-heritage backgrounds did not differ. As expected, sibling pairs who were reported to collaborate on their own initiative in family household work, without being asked, were more likely to collaborate fluidly as an ensemble in the planning task ( r = 0.44, P = 0.007, combining the three backgrounds). In turn, sibling pairs whose chores at home were reported to be based largely on adult control more often divided decision making into a solo activity, with one child bossing and the other simply implementing the plan ( r = 0.48, P = 0.002; nonparametric tests showed similar correlations). There were no other significant correlations between the pairs ’ ways of con-tributing at home and in the planning task. The relation between collaboration at home and in the planning task was primarily related to the children ’ s cultural backgrounds. When cultural background is controlled for with partial correla-tions, the significant correlations given above between ways of engaging at home and in the planning task become marginal: r = 0.21, P = 0.10 and r = 0.29, P = 0.07, respectively. The sibling pairs generally collaborated either in both places or in neither, following a similar approach across the two situations, and their approaches clustered by cultural background. The US Mexican Indigenous-heritage siblings (and to some extent, the Nepantla pairs) tended to pitch in voluntarily, collaborating at home, and to collaborate with each other fluidly in the planning task. The middle-class European American pairs tended to rely on adult control for their contributions to household work and to divide decision making into solo planning (often with one child controlling), not collaborating. Details of the cluster results are in SI Appendix . Cultural Values and Expectations of Collaboration Without Being Asked. We explored the role of mothers ’ cultural values and ex-that when we go to Mexico, that my daughter pitches in. She helps my mom clean her house, clean the bathroom, sweep, and I like that they see how they can help ” [our translation]. In fact, 42% of the Mexican-heritage mothers (four US Mexi-can Indigenous-heritage and seven Nepantla mothers) volunteered that it was beyond important for children to help without being asked — it was expected. (Their children ’ s approaches to the two situations did not differ in any obvious way from those of the other Mexican background children.) Some US Mexican Indigenous-heritage mothers stated that there was no merit in helping only when asked, and therefore it is important for a mother not to assign work. For example, “ It is important because that way, one knows that helping is coming from them ( ‘ les nace del corazón acomedirse , ’‘ it is born from their heart to help without being asked ’ ) and that there ’ s no need to be telling them ‘ Take the trash out, mop, clean. ’ And that they by themselves are starting to help. ” None of the middle-class European American mothers said that helping without being asked is not only important but is simply expected — unlike the 42% of the US Mexican-heritage mothers who volunteered this, χ 2 (1, N = 39) = 7.66, P = 0.006. In fact, 31% (4 of the 13) middle-class European American mothers but none of the Mexican-heritage mothers reported that it is not expected or important or even realistic for children to help without being asked, χ 2 (1, N = 39) = 9.23, P = 0.002. For example, “ Ican ’ teven imagine! Like, kids just doing chores without being asked?! That sounds very strange to me! ” (These four mothers ’ children used very little fluid collaboration as an ensemble in the planning task, averaging 13% of the time segments compared with 33% for the other nine middle-class European American children, and usually divided decisions, in 54% vs. 31% of segments.) The comments of the mothers who said that helping without being asked is important also had a different flavor in the two cultural backgrounds. Of the 26 Mexican-heritage mothers who said this, 12 focused on the importance of children ’ s help without being asked, for the benefit of other people, and only one fo-cused only on the children cleaning their own room. But of the nine middle-class European American mothers, only one fo-cused on children helping other people, and two focused on self-care (cleaning up their own mess or packing their own back-pack). Further, two of the nine middle-class European American mothers who thought it was important indicated that their chil-dren were too young to actually help without being asked; none of the 26 Mexican-heritage mothers said this, and one mentioned the importance of children learning this from the beginning. Many of the Mexican-heritage mothers described helping without being asked in moral or social terms. Three explicitly said that it is important for being good, moral people, and seven explained that helping other people without being asked helps people be well received and appreciated everywhere. For ex-ample, “ I always tell them, ‘ My parents always told us, be aco-medidos — wherever you go, there will always be a place for you. ’ ... My dad always said, ‘ Even if people don ’ t have enough food, but if you get there and help without being asked, they will share their food with you. ’” No middle-class European American mothers mentioned any moral, social, or community-minded reasons for helping out. In sum, the mothers ’ cultural values and expectations of children ’ s collaboration without being asked fit with the patterns that their children showed in their ways of being involved in household work and in the planning task. General Discussion Our primary finding was that in the planning task US Mexican Indigenous-heritage sibling pairs spent twice as much time as middle-class European American children in collaborating flu-idly as an ensemble, blending agendas in a flexible and co-ordinated fashion. Our findings extend previous research by distinguishing fluid collaboration as an ensemble from two other Alcalá et al. pectations to collaborate by asking, “ Is it important for you that children help without being asked? ” We also examined the mothers ’ reasons if they provided any. All 26 Mexican-heritage mothers from both backgrounds reported that it was important that children help without being asked. For example, “ Formeitisveryimportant ... to help, spontaneously help with something. There are kids that don ’ t do that. I am very pleased 11382 | www.pnas.org/cgi/doi/10.1073/pnas.1805707115