While it is assumed that the key solution to curb crimes is to educate prisoners about working skills, I do not think that it is rational to attribute pervasive criminality solely to illiteracy and therefore regard vocational training as the panacea to constrain the trend.
Indeed, it is easy to understand why this opinion in question is favored by some people. From their perspective, the major reason leading to illegal activities is the lack of schooling: it is true that many offenders embark on the path of crimes (e.g. theft, robbery) because they do not possess the needed degrees or basic skills to find a job; unfortunately, pure imprisonment does little to change their lives after releasing. In this sense, to train them basic vocational skills in prison seems to be a fundamental solution to prevent them from committing the same crimes after release.
However, it is not justified enough to recognize education as the key method to constrain the criminal activities. It is oversimple to attribute crimes exclusively to lack of education. Rather, the worrying trend is a complicated problem which is caused by various culprits; for example, the detrimental impact of media that makes young people aggressive and violent, and the many financial frauds are committed mainly by those with professional backgrounds. In response to these problems, multiple measures are needed instead of solely relying on vocational training. As an alternative, the government can institute laws against violence and obscene contents on TV and computer games, mitigating the possibility of young minds being exposed to offensive contents and therefore translating the plots in the virtual world into reality. As well as the media censorship, social service can play a part in cultivating a sense of social responsibility among those criminals with higher education. Both practices seem to have equally effective influence on crimes as educating prisoners.
In conclusion, it looks simplistic to assume improved education as the best way to limit crimes, whereas other options might be equally effective in tackling the problem.