The document is a letter from a mathematics teacher recommending a student take Calculus Research Lab (CRL) along with AP Calculus. CRL is a half-credit honors/AP course that uses computer algebra systems like SAGE, OCTAVE, and R to solve calculus problems graphically, numerically, and analytically. Topics covered in CRL include functions, limits, derivatives, integrals, sequences, series, differential equations, and more. The teacher strongly recommends the student take CRL to deepen their understanding of calculus and gain experience with scientific computing environments.