The more often one checks, the better.
I check mine umpteen times per day, and my control couldn't be better. (Though in part, that's on account of what I eat: quite a lot of rye bread, mostly with pear and apple spread, eaten steadily throughout the morning and into the late afternoon.)
To obtain the blood-sample, I never use those nasty spring-loaded gadgets - they're far too severe. I just gently jab my finger with a bare lancet - it's simpler, quicker, and gentler.
I also don't bother with a meter, most of the time. (I tend to use meter-read sticks only first thing in the morning and last thing at night.)
Instead, I mostly use visually read strips: Betachek Visual - which can be purchased here:
http://www.betachek.com/uk/store
They are on the UK Drug Tariff, but there is currently no UK supplier.
Each strip can be cut with scissors, so the cost per test is a few pence.
Because they're read visually, I find they give me FEELING for the state of things.
And feeling for one's condition is, I believe, especially important for a child with diabetes to develop.
If you buy two tubes, and keep the bulk of uncut strips in one of them, then your son can keep the other tube (containing a few striplets and a lancet) in his pocket.
Machines are fine, if they're needed. But why should anyone - especially a child - carry a meter around if it's not really needed?
If your son's blood-sugar is not well controlled, then the visually read strips will not be much use: for anything over 8mmol/l, they're won't give a clear reading.
But below 8mmol\l, they are really quite accurate. And the lower the blood-sugar, the more accurate the reading they give.