I regret I've lost the study (observational, not experimental) on students in North Rhine Westphalia on long term effects of early reading instruction but it showed children who learned to read later doing better at 16 or 17 than the ones who learned to read earlier. I think it was published in an economic of education journal but that's all I remember.
Edit:
The below study shows tiny differences between performance/school readiness of French and German children on entering primary school despite the French system being much more school like and placing a much greater emphasis on reading. Italics in abstract not in original.
French nursery schools and German kindergartens: effects of individual and contextual variables on early learning
Eur J Psychol Educ (2011) 26:199–213 DOI 10.1007/s10212-010-0043-4
The present article investigates the effects of individual and contextual variables on children’s early learning in French nursery schools and German kindergartens. Our study of 552 children at preschools in France (299 children from French nursery schools) and Germany (253 children from German kindergartens) measured skills that facilitate the learning of reading, writing and arithmetic at primary school. We also evaluated educational family practices and parents’ expectations of their children’s pre-school education. In order to take into account the hierarchical structure of our data, multilevel models were used in the analysis, which was carried out using MLwiN software version 2.02 (Rasbash et al.2005). Although French nursery schools emphasise academic learning, we did not find any significant differences in overall performances between the French and German samples. However, significant differences were obtained for some subscale results. In addition, our results indicate that individual and contextual variables have an impact on the differences observed between children from the two countries.