Is it allowed to use money from maser to give chanukah gelt to boys rebbei’s ?
It is permitted to use maaser money when giving money to a child’s rebbi as Chanukah or Purim present. Although it is a widespread custom to do so, and parents like sending the rebbi money in order that he should give extra attention to their child, nevertheless the parent is not obligated to do so. Therefore, one may use maser money for it. (It is understandable that this is only if the rebbi is eligible to receive tzedakah, which unfortunately is often the case.)
B’orach Tzedakah 11-48 quoting the author of Avnei Yoshpe.