It is a basic principle in the laws of tzedakah that this crucial mitzvah can not be fulfilled by spending in areas when one is already obligated to do so1. While buyin zuzah for a friend living in subsidized housing would qualify as tzedkah that same mezuzah for ones own home is part of the mitzvah of mezuzah, not tzedakah. Tzedakah in other words must be part of one's discretionary spending. As it is obligatory for parents to provide their children with a Jewish education it follows that tuition can not be considered a form of tzedakah. Thus those who can afford to do so must ignore their high tuition fees in calculating their tzedakah obligations. Of course a donation to a Jewish school so that others may attend would certainly qualify as tzedakah.
The Talmud states that technically a father is only obligated to teach his son some basic Tanach2 , (not Talmud) and has no obligation to teach his daughter3. Thus while one may have argued educating one's daughters and providing for ones sons post elementary school years - not to mention a year in Israel - is beyond one's obligation Rav Moshe Feinstein ruled4 that in our generation this is no longer true. While in previous generations education was for the purpose of obtaining knowledge, - religious observance was learned in the home - in today's environment education is the cornerstone of Jewish identity and a necessary ingredient in the fight against assimilation. While in Eastern Europe many pious Jews may have been quite ignorant in today's world it is next to impossible to produce a committed yet ignorant Jew. Thus the huge expenses in giving a child 10-15 years of intensive Jewish education is obligatory and should not be deducted from other charitable giving.
This ruling would seem to place an enormous hardship on many families - struggling as they are to pay the basic tuition costs of our day-schools. To turn around and tell them that they have yet to fulfil the mitzvah of tzedakah would seem to place unfair financial strain on an already depleted budget. Jewish legal authorities were well aware of this dilemma. They ruled that the mitzvah of tzedakah only begins after one's basic needs are taken care of5 . If after providing for food, clothing, housing and Jewish education there is little left over, one would actually be exempt from the key aspect of the mitzvah of tzedakah, namely the obligation to donate between one fifth and one tenths of one's net income to an appropriate cause. In fact it would be forbidden to donate large amounts of money and then apply for a subsidy, as this would effectively mean asking a school to fund your tzedakah preferences.
Those who truly can not afford to pay full tuition should not be sponsoring lavish kiddushes, taking out ads in dinner journals, or even giving large amounts to Israeli causes or UJA. Nor should they be spending money even on enhancements to mitzvoth, for example buying children their own lulav and etrog set. It appears to me that for those fees for which one is obligated to contribute such as schools, shul membership or mikvah upkeep - should each be paid a similar percentage of the amounts due.
Nonetheless, even someone on tuition subsidy must give at least token amounts to tzedkah6. This is so because the mitzvah of tzedakah has two basic components. First and foremost we must help the needy. And if that means sacrificing some luxuries so be it. Additionally the act of giving to others - irrespective of the actual amount - inculcates within us the trait of chesed (kindness) and serves as a crucial reminder that whatever little we have is a blessing from G-d.
1 Shulchan Aruch (SA) Yoreh Deah (YD) 249:1
2 Kiddushin 30a
3 Ibid 29b
4 YD#2, 113
5 SA: YD,251:3
6 Ibid 248:1