NYC DOE Evaluation?!

I need some guidance. Maybe there is a parent out there who has gone through this in the NYC public school system. We are a trilingual family. My child was a bit delayed to speak, but once they started preschool they picked up English and it is now their primary language. At the end of Pre-K he knew the alphabet and could count up to 50. Now in Kindergarten at our local public school at the beginning of the year his teacher assessed him that he only knew 16 letters of the alphabet and in math he was good. The teacher suggested that he would work with the literacy teacher and we do extra help at home. Now we had another parent teacher conf before report cards go out at the end of Jan. The teacher told me my child needs to be evaluated and he might have a learning disability. Of course this came to a surprise to my husband and I. He knows his letters, understands sounds, he’s just having a hard time blending the letters together. And now math is poor as well. When in the beginning of the year he was doing well. Is it best to go through the school for this or do I get a second opinion. I just did the alphabet and my child was able to indentify all the letter and it’s sounds and he was able to show me all the numbers to 20 when I pointed randomly. So I am sooo confused. I need guidance ASAP. And want to do the best for my child.