students (in both treatment arms) relative to students in the control condition (rather than, say, have no significant impact at all).

Perhaps a more plausible explanation for the negative effect of our intervention on grit-interest may be the content of the intervention itself, and in particular the deliberate practice component. Recall that the intervention induces students to update their beliefs about the expectancies and values of deliberate practice while studying, and in doing so, to motivate them to take up this particular form of practice. The rationale is that, when students take up this form of practice and experience a first “academic success” (which becomes more likely the more students practice), this will, in turn, reinforce their beliefs, leading to sustained behavior change and potentially long-run benefits. Deliberate practice consists of four elements: _(i)_ identifying stretch goals, _(ii)_ getting feedback, _(iii)_ concentrating fully, and _(iv)_ repeating until mastery. It is plausible that, when applied repeatedly to the same (or similar) stretch goal, the repetitive nature of these elements may crowd out interest in long-term goals – a potentially unintended consequence of deliberate practice itself. In fact, Duckworth et al. (2011), Ericsson (2006, 2007, 2009), and Ericsson et al. (1993) point towards negative “side effects” of deliberate practice, in the sense that this particular form of practice may be perceived as more unpleasant and exhaustive than other forms. <mark>This could also be reflective of the intervention not intentionally targeting a specific interest, as well as of the varied interests corresponding to the age of the children participating in the intervention.</mark><sup>24</sup> <mark>Developing consistency of interest among young children may, paradoxically, require diversification (sampling) of interests earlier in life.</mark><sup>25</sup> In sum, we find that our intervention induced students in both treatment arms to update their beliefs about deliberate practice relative to students in the control condition, with stronger effects when teachers deliver the curriculum as opposed to student self-learning. Impacts on grit are mixed: while students in either treatment arm report more perseverance-of-effort aspects relative to students in the control condition, impacts on consistency-of-interest aspects are negative, pointing towards the possibility of unintended consequences, and in particular, the possibility of crowding out <mark>of long-term goals-orientation.</mark>

# _Index of Socio-Emotional Skills_

As discussed above, we collected survey data on various other measures of socio-emotional skills. As all of them focus on some element of self-regulation, in our main analysis, we look at a single index (S/E skills) that combines the measures of deliberate practice beliefs, grit, frustration reaction, motivational frameworks, locus of control, and present bias, to reduce dimensionality and multiple hypotheses testing.<sup>26</sup> But before proceeding to this analysis, we first have a look at the _relative_ importance of different sets of skills, in particular deliberate practice beliefs and grit _versus_ all others. Table 4a shows the impacts of our intervention on our S/E skills index on average (Column 1), when excluding deliberate practice beliefs and grit (but including all other skills) (Column 2), and when including only deliberate practice beliefs and grit (excluding all others) (Column 3).

> 24 See, for example, Sturman and Zappala-Piemme (2017).

> 25 See, for instance, Gopnik (2020).

> 26 Appendix 1 Table A1.2 replicates Table 3 and shows findings for frustration reaction, motivational frameworks, locus of control, and present bias.

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