Time will heal all but if you want to help your youngster make a quicker adjustment you can give him 2 Bach Flower Remedies: mimulus (for separation problems) and walnut (for adjusting to changes). Check out www.bachcenter.com for information about the remedies; you can find them on-line and in health food stores.
In addition, you can use emotional coaching (see the MP3 download on this site or look in the book "Raise Your Kids without Raising Your Voice." By naming and accepting his feelings, you'll be helping him a lot.
Feel free to give him rewards for courage as well. When you drop him off, leave him with a little treat (food, a toy, a comfort item or something to ease the transition).
Sometimes having someone who is not the mother (or parent) drop the child off eases the difficulty of separation as well. I don't know if there is someone else who can do it, but if there is you might try this also.  All the best,  Sarah Chana

My kid did the same for 2 months and then settled in beautifully. Just wait it out.

I think most kids this age have some trouble with separations. They do grow out of it. Just be patient. I don't think there's much you can do about it.