Oh noooo!
Shawna, did YOU talk with the teacher to ask for help with Jake on Monday? I know she'll have her hands full, but maybe she's got some tips.
Basically what I remember from daycare drop-offs, you want to keep your drop-off as quick as possible, don't linger and don't cave in to their unreasonableness. Remind them when you are coming back to get them (is it after lunch? After recess? Some kind of time marker for him) and be as confident and cheerful as possible.
Maybe there will be another neighbor kid in his class? Even if it's a girl, it will be someone he knows.
DS4 was crying and very clingy at the preschool drop-off at the beginning of the school year last year, and it broke my heart. But I knew (having gone through many daycare drop-offs with DS7) that it's a very brief phase they go through.
I sobbed my way through DS4's first day at preschool, then rushed to the school to pick him up. He was totally happy by then, of course (and I'd had a terrible 2.5 hours myself!) The next day he still cried but not as hard, and by the 3rd day it was like he was just putting on a show for my benefit, he really just wanted to go play with the kids.
Jake will be fine, kindergarten is very much like preschool so the routine will be familiar to him. I would have been nice to have a little 1-on-1 with the teacher beforehand so Jake could have said hi and spoken to her a bit. Ah, well. It may be bumpy on Monday, but it will get better!