"Many a forenoon have I stolen away, preferring to spend thus the most valued part of the day; for I was rich, if not in money, in sunny hours and summer days, and spent them lavishly; nor do I regret that I did not waste more of them in the workshop or the teacher’s desk." Explain this quotation. Be sure to address the “wealth” Thoreau claims, his use of that wealth, and his views of the workshop or school.

Essentially, Thoreau is saying that his time spent in nature has been a better use of his time than working or going to school.
The quote specifically mentions that Thoreau liked to go out before noon. This is when he would "steal away" in order to be out and about in nature. Thoreau is a transcendentalist, so spending time alone in nature is akin to a Christian spending time in prayer or at church. Thoreau is communing with nature, and he states that this time has made him a wealthy man. He freely admits that the wealth is not a monetary wealth. He is rich because he is in harmony with nature's beauty. He bathes in the sunlight and free time, and he doesn't regret doing it either. He feels that his stolen time with nature was far more valuable than slaving away for a paycheck in the workshop or spending time in the classroom either learning from a book or teaching other people. For Thoreau, experiences are far more valuable, and experiences with nature hold the most value.