Reiki classes have quite a job to do to impart the wisdom of Dr. Mikao Usui. While the Usui method is the basis for the practice of Reiki energy healing, since it's inception more than thirty variations of the original theory have risen up. You'll need Reiki classes that accept and explain these different variations to arrive at a feasible method of teaching.
With the proliferation of online websites regarding every possible topic, there is a wealth of information--and misinformation--about Reiki. Look for a well-regarded school with a large constituency of online members--such a community can act as a sort of system of checks and balances. An active, engaged community will hold the the school it associates with to high standard, while also acting as an invaluable resource to the Reiki student.
Reiki Classes as a Facet of the Wicca Craft
Wicca and Reiki actually have much in common, and it makes sense that the two would be offered as part of a comprehensive course of study. Both belief systems emphasize the role of harnessing the earth's energy as a path to spiritual fulfillment. Such lessons, in whatever format, can greatly increase one's quality of life.
Another similarity between the two is the theory that inner harmony is possible for us all. One need not possess intrinsic, natural gifts to succeed along the Path. All it takes is an open mind and heart, and a willingness to persevere through the process of learning.