I just took class at work on the GE Mark IVe controls. It was funny because some of the people in our process control group (the group that deals with our DCS and PLC's) struggled. A few of us field technicians did really well, but I think it was because we didn't know any different and weren't used to working on other systems we had.I hear this same question asked over and over on different forums, because I believe people without past PLC knowledge have some misconceptions.
PLC is a generic term- way to broad in scope.
Because every manufacturer of Programmable Logic Controllers has their own entirely different software, each is quite unique. To learn Siemans S5 or S7 is great, but you will not have a clue about Allen Bradley Contrologix much less anything about an antiquated Square D platform.
Each must be learned on their own.
The thing you should be learning is ladder logic, and Boolean math. These are the basics of all PLC's.
Just getting "on-line" to monitor I/O with a manufacture you are unfamiliar with can be a trial, much less doing any programming.
So before you spend good money taking a class, know what manufacture you will be dealing with and save yourself some headache.
Every system is different, but I agree learning the ladder logic and boolean math is a great start.
The question is what kind of training to you want for PLC's and what do you want to do with it? Do you want to be a programer or do you want to work on and maintain them?
I don't have any experience programing, but on some systems I can get into programs and use it to help me troubleshoot field problems. I can also apply forces if needed.
I wouldn't spend a ton of money on any class unless you know you will get a return on your investment.
If you can get a job where you work around them, that would be your best stepping stone.
Try to find a cheap class to learn the basics. If you have something on your resume it may help you get your foot in the door somewhere. When you get your foot in the door you will have a better idea of what you need and can work from there.