Looking back on my school years, your guidance was like sunlight breaking through clouds on a rainy day.
I'd suggest something like 'Your lessons were the compass that guided me through stormy seas of adolescence - thank you for being my North Star.' It captures gratitude while acknowledging their role in shaping your journey. For a lighter touch, 'You turned quadratic equations into adventures and Shakespeare into my secret language - that's real magic!' works well too.