I don't have any research, but I can tell you anecdotally that that system was horrid for one of DS8's friends.
We've never dealt with it personally (we've only done Montessori but one of his good friends started at a Catholic school. I've watched this little girl and I have to say she is one of the most well behaved kids I know. She's bright. She listens to reason. And she's cooperative. She almost got kicked out of school because of the effects of the this system and ended up switching mid-term to the Montessori.
For her, it made no sense. Like you said- the warning might have nothing to do with why she got the yellow. And neither infraction had to be a big one. In fact, in the early weeks it struck me (from her mom's stories) that they were just trying to get them good and afraid of getting yellow or red so they were very liberal with handing them out. The girl started out trying to reason with her teacher (hah- that went over well.). Then she sincerely tried (per her mom's direction) to try harder and accept any punishment. But after awhile the unfairness that she perceived just made her lose it. She drew a yellow and screamed "I don't deserve this.". That comment got her a red and she fell to floor screaming and wouldn't get up. Several parent conferences about what was "wrong" with her and another episode of her melting down about getting a yellow (and subsequent red) and the school was making suggestions that she might need a different environment. Her parents pulled her out and put her in the Montessori with my son. The director was nervous to have her given the past "emotional problems" she'd displayed. But she flourished there and never had a single meltdown.
Montessori comes with its own slew of problems- dont get me wrong. But the lack of that system is one thing I am grateful for. By the bright and gifted child it is quickly (and correctly) perceived as unfair- particularly in the hands of the wrong teacher. Wishing you the best in trying to help your son navigate it.
