They didn't start tracking in 1983, the numbers I linked start in 1971. The trend line is pretty much the same from 1971 to 1983 as it is from 1983 to 2006. In any case, a skeptical person would not look at that graph and say that there was a successful effort to improve childhood literacy represented on it.

It's true that we don't know the counterfactual: it's possible literacy would have plummeted precipitously starting in 1984 if Reading Rainbow hadn't been a bulwark. But I don't find that the most likely explanation, personally.