Hi Daisy, no excuse! ;-) One of the tips we give folks taking ukemi for koshinage is to look at nage the whole time as you're going over - a great tip when taking any kind of high breakfall - it turns you in such a way as to protect your head. "Thinking light and responsive" also helps and reaching far back with your free hand (so that your hand hits the mat before the rest of your body) helps absorb the impact so that it's less punishing. Good luck!

Practice koshinage ukemi over a static nage's hips. get your center over their hips and snake your arm on the side opposite their head across/under their body and grab their uwagi on the far side (the side you start on). That will help you "get over" and prevent you from going in head first.

OK, this is a coincidentally very timely post. 1.) It's true, I wasn't in class on Tuesday! I had a DMV appointment! 2.) I know all about those spongy teenage students. Sometimes they are sticky, too. 3.) Koshinages terrify me. Precisely b/c, even though I am not short of focusing, I feel all the time like I'm getting spiked headfirst into the mat. And squished like a bug.