Treat adult students as adults. Children and teenagers tend to need a lot of praise and reaffirmation, especially in art classes where they may feel insecure about their skills and techniques. To an extent, adult students may also need encouragement, but excessive praise may seem patronizing. Refrain from giving adult students exaggerated praise as you would children. Most adults are mature enough to handle honest and frank feedback.
Explain criticism. When pointing out flaws and problems with a student's work, explain methods and techniques to overcome such issues. Adult students, unlike young learners, won't perform a certain way simply because they're instructed to. Adults want to understand why a certain method or technique should be used. For instance, don't simply tell an adult to use a different brush stroke; demonstrate how a different brush stroke is more suited to the task.
Be patient and urge suggestions for improvement. Adult learners tend be more self-guided than young learners, often resisting instruction because they trust their own instincts and inclinations. Therefore, you may need to emphasize, reinforce and remind adult students about techniques and methods to improve their work before they begin to incorporate your feedback.
Learn about adult students on the first day of class so that you understand what skills and talents they bring to the table. Find out their professions, hobbies, experiences and skills. Ascertain what prior experience and education they have with painting or other areas of art. These personal details will help you to understand their learning strengths and weaknesses, enabling you tailor your instruction to their needs.