The paper presents the use of spreadsheets integrated with digital tools capable of symbolic computations and graphic constructions in a master's level capstone course for secondary mathematics teachers. Such use of spreadsheets is congruent with the Type II technology applications framework aimed at the development of conceptual knowledge in the digital era. The paper reviews educational documents developed worldwide that set standards for teaching mathematics and offer recommendations for teacher preparation. In particular, these include Common Core State Standards and the Conference Board of the Mathematical Sciences recommendations for high school teachers, the most recent guidelines for mathematics educators in the U.S. A course assignment associated with extended explorations of Fibonacci numbers that connect undergraduate mathematics coursework and school mathematics curriculum is presented along with the author's analysis of the teacher candidates' reflections on their work.