This is a great time to be considering what assistance or teaching he needs to finish kindergarten well, what he could benefit from this summer, and how he could be well-supported next year. I would suggest you:
1. Speak separately to each person who works with him (teacher, speech therapist) as well as the school's team chairperson. These conversations, with lots of listening on your part, will enable you to gather different perspectives on how he learns best and ways to enhance those ways.
2. Start taking notes on all you learn.
3. After your conversations, start to think about which person is most likely to be able to help you, as the key person may be different depending on the student, the parent and the staff. This person may be your guiding light for years.
4. Then request the school initiate a full evaluation of his needs and strengths, including cognitive, language, social, etc.
I think I remember that you kept your son out of kindergarten for a year, to let him be ready, so now is the perfect time to let the school know that your concerns are valid and need to be addressed. All my best.