An single extra unit (or less) of insulin can kill a type 1 diabetic. I don't expect non-diabetics to understand what that means, but it's not more than a few drops of insulin.
What ISF does your kid have that a single unit will kill him/her? A single unit is barely noticeable on the graph for me.
I've been using Loop for a few weeks now and the improvements in quality of life are so huge that any concerns I had about safety went away. Reading the docs, which are a great example on how documentation should be written, helped a lot with that too.
The typical level of sensitivity is absolutely in range for a single unit to produce a catastrophic event.
It sounds like you may have a low sensitivity factor. The usual starting point for estimating this, along with using the "1800 rule", puts typical sensitivity around a drop of 50 points in blood sugar for every unit of insulin. This based on a weight around 65-70 kilos and 0.5 units/day/kilo.
Of course it depends on other details too, even time of day. (My wife, who uses a medtronic pump, clocks in at right about this level but is less sensitive in mornings and more so later on. her pump is programmed for these time-dependent sensitivity fluctuations )
This level of sensitivity absolutely has lethal potential with a single-unit swing. If you're in the low end of normal at 75 points and take another unit dropping it to 25, this is plenty low to cause a person to pass out and thereby be unable to take corrective action, with lethal consequences, especially if the pump is still delivering a basal dose inching levels even lower.
You might argue that careful people shouldn't encounter this situation, and you'd be right. But it still can and does happen, meaning a hobbyist setup that gets something even a little bit wrong has that same potential.
I don't recall off the top of my head, but keep in mind he weighs roughly 50lb. As I mentioned in other comments, Tandem's coming out with their equivalent of Loop (called "ControlIQ") in the 2nd half of this year, so I'd obviously prefer a supported solution. Plus, it's unlikely the school system is going to be willing to have anything to do with a non-official system.
What kills is an unchecked persistent low blood sugar causing confusion, black out, coma, and eventually cardiac arrest.
A single unit of insulin in isolation, to a T1D with undepleted glucagon stores is going to cause a low but won’t result in a black out.
A single extra unit of insulin, to a small child, who just completed a long day of exertive activity, and who had lows earlier in the day which drew on their body’s natural glucagon store, and who is not being monitored by a third party, that could be dangerous.
Keep in mind the accuracy of dosing with a syringe is not much better than +/- 0.25 units, this is why continuous monitoring is so crucial. You never quite know how well the insulin is absorbing, how well the carbs are being digested, maybe even how many carbs exactly were ingested in the first place.
For a small child with a carb ratio of 30g/unit (1 unit of insulin “covers” 30 carbs) and a sensitivity upward of 200/unit (1 unit of insulin without any carbs lowers blood sugar 200 points), being dosed by syringe, without a CGM, you are fighting lows pretty regularly and have to be able to recognize and treat them (glucose tabs, juice, cake frosting when things get more serious, and glucagon injection when things get critical).
I’ve never had to gluke my kids, but the day will likely come. We carry glucagon, juice boxes, and tabs everywhere.
T1D is potentially life threatening pretty much every day. You do the best you can with the tools you have to keep blood sugars in range without too many lows (too high is long-term bad, too low is short-term bad).