Our study on 328 five- to six-year-old kindergarteners (mainly White European living in France, 152 girls) shows that children who do not count on their fingers and undergo finger counting training exhibit drastic improvement in their addition skills from pre-test to post-test (i.e., accuracy from 37.3% to 77.1%) compared to a passive control group (39.6% to 47.8%) (p < 0.001, [partial eta-squared] = 0.15). This result was replicated on a much smaller scale (37 five- to six-year-olds, mainly White European, 22 girls) but in more controlled setup and was further replicated with an active control group (84 five- to six-year-olds, mainly White European, 37 girls). Therefore, we demonstrate here for the first time that training finger counting constitutes a highly effective method to improve kindergarteners' arithmetic performance.