We will be traveling in Scotland the last couple of weeks in May. Do you think it is necessary to book accommodations ahead of time in North Highlands?

Yes, book ahead. We only went as far north as Lochinver, and even booking ahead the pickings were slim.

The end of May has a Bank Holiday so any dates close to that weekend really need to be pre booked. Where exactly are you touring? In many areas accommodations are few and far between so I would not want to be in for example far NW Scotland w/o knowing exactly where I'd be sleeping. Also Skye has become insanely popular, so really MUST be booked ahead. In 'tourist central' towns (Inverness, Ft William, etc) there are enough hotels/B&Bs that you can find places at the last minute . . . Though I personally would not stay in either town.

So -- your question is really not fully answerable w/o knowing what parts of the Highlands you are talking about and your actual dates.

Also the last week of May falls during school half-term holidays in UK.

Having now seen your other thread -- you have maybe more issues that whether you need to pre-book. Your plans are really REALLY aggressive. But at any time, even without the added pressure of the Bank Holiday/half term, one would definitely want to pre book on Skye, in/near Ullapool, on Orkney, on Mull, etc.