Financial Statement Analysis
Since the raw data for valuation comes from financial statements, being able to read financial statements (income statements, balance sheets and statements of cash flows) will help a great deal when you actually have to value companies.
Basic Statistics
Students should have an understanding of basic statistics, from how to summarize data (with statistical moments) to how to analyze relationships between variables (correlation and regression).
Time Value of Money
Understanding why there is a time value for money and being able to move cash flows across time (by discounting and compounding) is an essential component of valuation. This may be as simple as understanding how to use present value equations or functions.