To Retain or Not to Retain

Hello! I have a 5 year old currently in Kinder who is "behind academically." We went from a Montessori preschool from ages 3 and 4 to a private catholic school (big change, I know). His teacher is suggesting he repeats Kindergarten because he is far behind his peers academically. He is one of the youngest (late May birthday) in his class and she believes that maturity plays a huge role here. I have been working with him at home for months on his letter sounds and phonics and we have not seen much improvement. He is tested on words like "floss" and "stiff" (that's a big word for Elmo in my opinion) and bombed a literacy test that was given to him on a computer (I'd like to add. That was his very first time using a computer ever). He does well in math and actually enjoys math and is super social and loves his friends. Maturity is an issue since he does have frequent meltdowns and is a frequent daytime wetter.

What are parents doing in situations like this? I am reading so many conflicting things. Should we do another year in Kinder? That would mean him losing his friends and we'd pay for an extra year of school. Should we send him to first grade at public school? What would you all do?

*********Update:

We are going to get him assessed for autism/ADHD and will make a decision after that.

I talked to his teacher today & she does believes that he grasps the academic concepts just fine (but just doesn’t perform at school for whatever reason) but his maturity level is the MAIN concern for her.

Once we get feedback from the specialists, we can make a better, more informed decision. I am not sure how long this will take but we all agree that if he does have autism/ADHD, he would be better supported in public school. I have consulted another pediatrician who focuses on development regarding the daytime wetting and he will be seen by her later on this month. Thank you all for the advice! I truly do appreciate every comment even if I seemed a bit defensive. I want the best for my little munchkin and will support him with everything that I have. I hope that anyone reading his and wondering what to do with their little one is able to get some wonderful advice as well.