In Russia, Kazakhstan and Belarus
Russia
The limit is 150,000 ₽ a year for all such expenses together (Art. 219 of the Tax Code, «НК РФ»), plus 110,000 ₽ separately for each child's education; expensive treatment has no limit. It is claimed with a 3-NDFL return, through the employer or under the simplified procedure in your personal account.
Belarus
Belarus has social deductions from income tax: for first higher or secondary specialised education and for voluntary life and medical insurance.
Sources: Tax Code of the Russian Federation, part two («Налоговый кодекс РФ»), ConsultantPlus, Federal Tax Service of Russia («ФНС России»)