When I started out I had major problems with speed control. I always went off too fast and found I couldn't finish the runs. I eventually worked through it and learned to slow it down a bit.
I'm currently helping out on a C25K course and the leader has absolutely nailed it.
He paired everyone up, one person walks at a reasonable pace (not too slow, but not a route march) and the second person runs alongside them at the walking pace set by the first person. Swap over every 1-2 mins. The thing is that going forward you don't actually have to run any quicker unless you want to.
The only other thing to note is that while they are running he gets them to concentrate on decent posture and making sure their feet are landing under their bodies so they don't over-stride.
From the off he's teaching speed control and correct running posture which hopefully will become second nature for the new runners.
Hope this may help some of you starting out 👍