Answer: Without
seeing your son in person, it is difficult to assess what exactly may be
affecting his start-up speed. Still there are some basic things he should
concentrate on.
A common problem is improper body
position (i.e. standing too upright), without enough body lean. Proper
body position depends, of course, upon what sport and what position he is
playing so to make things simple, I'll make some suggestions assuming he
is a wide receiver on the football team and is starting from an upright
2-point stance.
He should take a position with
his chest over his feet, bent slightly at the waist/hips and knees and his
head up. As a receiver his feet should be slightly less than shoulder
width apart and comfortably staggered (i.e. the inside foot up and the
outside foot back several inches - inside refers to the position closest
to the ball - if he lines up on the left side, his right foot is his
inside foot, if he lines up on the right side his left foot is the inside
foot). His arms should be cocked and about waist high and in position to
pump when he takes off.
Often runners loose time by
standing up - not firing out at the start. Sometimes they will take
a step back. His first move should be out, not up. When he strides his
toes should be in line (not pointed in or out) and on a line midway
between his legs.
There are some drills he can do
to help improve his speed. Probably the best are power jumps.
First Step Drill
Starting from a good body position, practice making that first step a
strong step in the intended direction--first with the right foot and then
with the left foot.
Vertical Power Jumps
Feet shoulder width apart, bend at the knees and explode up as high as
he can and reaching up with both arms. Give him a target of some type (a
basketball hoop or even a marked pole) to reach for so that he can measure
his improvement over time. Repeat several times.
Power Broad Jumps
Instead of exploding up, good body lean forward with the chest over
the feet and explode forward, pump the arms forward as he explodes. He can
do single ones to start then string three or four together.
Another good drill that you can
have him do, with your assistance, is running forward with his eyes
closed. He should try to run in a straight line. Spray paint a line on the
grass or use a line on a football, baseball or soccer field. Make sure he
is in an open area and doesn't run into anything. This doesn't have to be
done at top speed, instead use a controlled speed. He should focus on good
body lean and visualize the placement of his feet - in line. Soon he will
be able to run in a straight line with his eyes closed.
Also have him run some drills
running backwards, picking his knees up high. This will help him
understand how important it is to have a good forward body lean.
Running backwards requires that he keep his chest out over his feet, so
that he won't fall backwards.

You did not indicate where you
live. But if you are in or around Northeast Florida, I know of a great
coach who runs speed and agility camps several times throughout the
year. His name is Darrell Pasquale. He has coached in the NFL with the San
Diego Chargers and at several colleges including Army and San Diego State.
His dad, Larry, coached for the NY Jets, the St. Louis Rams and the
Jacksonville Jaguars. They often work together at Darrell's camps.
I have attended Pasquale's
camp and have seen the improvements he has made for kids from 9 to
18 years of age. The suggestions I have made are based on conversations
with Darrell and techniques and drills he uses in his camps.
If you are interested in learning
about Darrell's Speed Camp, please let me know and I will send you his
phone number. I hope this
helps.