The general rule is that anything which is obligatory cannot be paid with ma’aser money, whereas voluntary contributions may be given from ma’aser.
When it comes to children’s education, some Poskim hold that for young boys, since their education is an obligation upon their parents, it cannot be paid from ma’aser, whereas for girls and older boys, since the obligation for their education does not fall on the parents, the costs can be paid from ma’aser. Nonetheless, if the child is studying in a yeshivah or such like that has a dormitory, since the costs of food and board are an obligation upon the father, he cannot pay that portion of the tuition from ma’aser money.
However, Rav Moshe Feinstein (Igros Moshe YD 2:113) rules that nowadays since education is government-mandated, tuition becomes an obligatory cost and cannot be paid from ma’aser money. Nonetheless, he writes that any tuition costs above what is expected from a person of his means a person may pay from ma’aser money; furthermore R’ Yaakov Blau (Tzedaka Umishpot 11 footnote 35) writes that it is commendable to gives one’s ma’aser money to an institution in which one’s children study.