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The other thing to consider is ski schools will effectively close before the resort does. So if you want to do a lesson, late March/early April are the latest you can go. Past 2nd week of April, Breck ski school closes and/or greatly reduces offerings.
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@dred pirate, no matter when you go, your novice wife will probably need to ski on beginner/novice terrain and she will want to take at least one lesson if not more.
In November and December, when coverage is iffy, some (maybe not all) mountains focus on opening their expert terrain first, and leave the beginner hill and easy greens for later. With that terrain not open, the ski school will probably not be offering beginner or novice lessons, although they may offer upper level lessons. Ski schools may also not offer the lessons you need when it's late season as well, as mentioned by @Selcomski above.
I'd suggest calling around now to the ski schools you are considering in order to find out what instruction is likely to be available before you decide to make this trip in November/early December, or in mid-to-late April.
If no one is there to answer your questions, there are ways to find historical information on when the mountains open, but not much is available on when the ski schools get their beginner terrain open. You'll need to talk to someone who works in the ski school, I think.