This is the most heated debate among softball pitching coaches. Do you focus on speed first and then control or control first and then speed? Every pitching coach has their own opinion but here is where I weigh in on the topic.
I believe in proper mechanics. With proper mechanics, speed and control can be achieved but more importantly the injuries will be minimized and hopefully non existent. When learning mechanics, it is important to get to full speed as quickly as possible. Going full speed is the only way you can teach "timing" and allow your arms and legs work together.
In my 13 years of training, I have found that no matter when you start pitching, you will not break much into the 50's until you are done growing at around age 13 or 14 with proper mechanics. My students who break that speed mark before 13 or 14 usually do not increase speed much after they get to high school. The reason is they usually do not have the proper mechanics and they have reached a limit to what their current motion can produce. Size and weight also influence speed.