After prayer was removed from schools, performance has declined and social problems have increased.
Many opponents of church/state separation allege that any growth in social ills like crime, drug abuse, and teen pregnancy are all due to the removal of government-sponsored prayer and Bible reading from public schools. If only these government-sponsored religious activities had been kept, so the argument goes, society would be better off. Therefore, we should reinstitute these special privileges for Christianity and save society from future grief. No part of this argument is true or valid.
Broadly speaking, this entire argument is nothing more than a logical fallacy: post hoc ergo propter hoc. Regrettably, it is a fallacy which is often committed by many people and in many situations. The nature of this fallacy is to assume that when two events happen around the same time, then one must be the cause of the other. It is for this reason that such a fallacy is often criticized as a failure to properly distinguish between correlation and causation.
To make it easy to see why the above argument is a fallacy, consider another series of momentous legal, political and social events which happened around the same time: Civil Rights and School Integration. How many opponents of church/state separation are willing to argue that the decline in school performance and increase in both school and social ills are due to Civil Rights and School Integration? Not many — but, from a correlative perspective, that is no less valid than attributing our social problems to the elimination of state-mandated school prayer.
It's also important to recognize that this argument aims at nothing less than wholesale privileging of Christianity by having the government sponsor, endorse, and/or encourage particular Christian religious practices. This argument doesn't lament any decline in religion, but rather a loss of government-sponsored religious practices in the past — and without even trying to argue that the government ever had any authority to write prayers or have students read Bibles.
The fact of the matter is, our social problems are complex, their origins are complex and their solutions will be complex. Even if the lack of official school prayers contributed anything at all to those problems, it would be invalid and simplistic to focus only on them as some sort of magic-bullet solution. As it is, no actual causal connection has been demonstrated by anyone — all people can do is point to a correlation in time and claim, without basis, that this alone justifies a causal relationship.