There is some confusion surrounding MacLaren tartan and scouting. All scouts, not just those with Wood Badge, are entitled to wear it, and this right was conferred by someone who was at the time both the chief of the clan and the commissioner of the Scouting Association (the UK member organisation of WOSM, just as the BSA is the US member of WOSM).

Wood Badge is offered worldwide as training for leaders in scouting (in fact it's the only scouting award that's worldwide), and entitles you to wear a scarf with a square of McLaren tartan, amongst other regalia, but you don't have to have your Wood Badge to wear this tartan in the form of a kilt, you just have to be in scouting.

My wife has her Wood Badge, FWIW, which she obtained as a BSA leader in the US, and is also a Queen's Guide (UK female equivalent of an Eagle Scout). OTOH, I never progressed beyond being a cub myself, and besides that have only been a merit badge counsellor and have never worn an adult leader's uniform. I suppose either of us would be entitled to wear the Maclaren tartan, but she can also wear a scout scarf with a patch of Maclaren tartan, whereas us lesser mortals can't.

Uniform rules are something else entirely separate from the right to wear any particular tartan, though. BSA rules don't recognise a kilt as uniform, but IME non-standard trousers and jeans are so common that I'm not sure it's a big deal. I suppose it depends where in the US you are located.

SA uniform rules on kilts in the UK are complicated. They allow kilts of any tartan for all scouts in Scotland, but in the rest of the UK outside Scotland you have to be of Scottish descent to wear a tartan kilt, and it must be either in your own clan's tartan or ... Maclaren.

The SA also allow plain saffron kilts for all SA scouts in NI and for scouts of Irish descent in the rest of the UK. However, Northern Ireland is also covered by another WOSM member organisation, Scouting Ireland, based in the Republic of Ireland, which appears to consider anyone wearing a troop scarf to be in uniform, although I think that for parades they require full uniform including regulation trousers.

I'm aware I haven't been consistent on how to spell McLaren/Maclaren/WHY, but I think they are all variations of the name.