A randomized control trial finds that CPS is as good as PMT.
CPS was developed by Ross Greene and is presented in the book "The Explosive Child".
Note that there is a split in CPS. Greene was forced out of the original Mass. General Hospital (MGH) program and he
was told MGH has the copyright to the name Collaborative Problem Solving. So Greene changed the name his version
a bit and kept the acronym. The MGH web site is here:
The CPS motto is "Skills nor Will". One can argue that PMT is all motivation and no skills training. CPS takes the position that kids with behavior problems are already motivated to behave well but they don't have the required skills.
However, when I analyze CPS, I see that their Plan C is equivalent to Planned Ignoring which is a component of PMT. Also, CPS rules dictates that the parent should not engage in problem solving as an immediate reaction to the problem behavior, again similar to Planned Ignoring. So, CPS, like, PMT avoids the common parenting practice of motivating unwanted behavior by reinforcing it with knee-jerk instant parental attention. CPS at least avoids inadvertent counterproductive motivation.
Also there are already studies of approaches that include skills training along with PMT.
Also, there more than dozen of RCTs of PMT. CPS is relatively new, PMT was used as a positive control in the study I cite at the top.
Also, this RTC might not be as independent of the CPS originators as one would like
That said, I think it's true that using only motivation can be a mistake, that sometimes skills training can be important. For instance, study skills and other learning strategies can be better than only trying to motivate reinforce or punish grade performance. Also the timing is all wrong with quarterly grades, too much time between the effort and the contingency. One might be able to motivate some short-term aspects related to school performance, at most.