WHEN DID GALAXIES START FORMING STARS? WHAT IS THE ROLE OF DISTANT GALAXIES IN GALAXY FORMATION MODELS AND THE EPOCH OF REIONIZATION? WHAT ARE THE CONDITIONS IN TYPICAL LOW-MASS STAR-FORMING GALAXIES AT Z ~ 4? WHY IS GALAXY EVOLUTION DEPENDENT ON ENVIRONMENT? TO SOLVE THESE PUZZLES OF GALAXY EVOLUTION WE WILL USE 41 GALAXY CLUSTERS FROM THE RELICS PROGRAM (REIONIZATION LENSING CLUSTER SURVEY) THAT ARE AMONG THE MOST POWERFUL COSMIC TELESCOPES. THEIR MAGNIFICATION WILL ALLOW US TO STUDY STELLAR PROPERTIES OF A LARGE NUMBER OF GALAXIES ALL THE WAY TO THE REIONIZATION ERA. ACCURATE KNOWLEDGE OF STELLAR MASSES AGES AND STAR FORMATION RATES (SFRS) REQUIRES MEASURING BOTH REST-FRAME UV AND OPTICAL LIGHT WHICH ONLY SPITZER CAN PROBE AT Z>0.5-11 FOR A SUFFICIENTLY LARGE SAMPLE OF TYPICAL GALAXIES. THIS PROGRAM WILL COMBINE SPITZER IMAGING FROM TWO LARGE PROGRAMS DIRECTOR DISCRETIONARY TIME (DDT) AND THE SRELICS PROGRAM LED BY THE PI. THE MAIN CHALLENGE IN A STUDY SUCH AS THIS IS THE CAPABILITY TO PERFORM RELIABLE PHOTOMETRY IN CROWDED FIELDS.