This just a suggestion. I have been in the Secret Ninja School for quite some time. I too used my Red Codestones for training. I was spending so many NP's to train I was ready to give up. Finally I started buying FQC's for training instead of the school. Every quest bumps your stats more than one point and most always includes more than one stat. Of course, this is something you already know but I thought I would mention it anyway. It really increased my bank when I started selling those red stones instead of using them.