Every person must seek and search very much for an honest, upright and God-fearing teacher for his children, and beseech G-d very much about this, in order that his children’s teacher shouldn’t corrupt the holy breath of the mouths of the schoolchildren, which sustains the world. (For due to our many sins, there now exist educational societies that aim to teach little Jewish children secular wisdoms – which are stupidity and darkness – as well as the languages of the gentiles (this subject is discussed in Likutei Halachot, Hilchot Pesach 7). These studies defile the holy breath of the mouths of schoolchildren, and as we ourselves can see, these children subsequently grow up to be atheists, heretics and the like. Therefore, Reb Noson writes there [in Likutei Halachot]: “Happy is he who keeps himself and his children far away from these people.” It is our duty not to send our children to such places. We should have no connection with them whatsoever.
(Kitzur Likutei Moharan, I, 37)