Ali Sina is an Iranian/Canadian ex-Muslim and critic of Islam. Frustrated by the whitewashed version of Mohammed presented to schoolchildren, he produced this honest biography. We suggest that it could usefully be presented alongside the usual course material for older children. It would doubtless lead to some interesting discussions.
[unfortunately this link is not operational at the moment. Ali Sina intends to fix it when he can]
On his Faith Freedom website Sina also features this abridged version of the earliest biography of Mohammed by Ibn Ishaq. This would likely be an eye-opener for any teacher prepared to go to the source.
NB The picture shows Mohammed presiding over the slaughter of 600-900 men of a captured Jewish tribe, the Banu Qurayza. The women and children were sold into slavery.