R. Pruzansky said “50% of the graduates of Modern Orthodox high schools are no longer Shabbat or Kashrut observant”. And in light of several posters explaining that this is because many Modern Orthodox families are not Torah observant in the first place, it is worth repeating DaasYochid’s rebuttal that R. Pruzansky’s article “implies that they once were Shabbat and Kashrut observant, unlike the theories put forth by some posters here.”
In other words R. Pruzansky is saying, if you read his words carefully, that 50% of once Torah observant Modern Orthodox graduates become no longer Torah observant.