School scores provide an objective measure. Then I recommend that you look at the individual schools and pick the one that has the best feel within the score range that you want. Of the schools in Carlsbad Unified School District, Kelly Elementary has posted very high scores repeated for years. This past year I think it scored the highest is CUSD at around 937. This was followed by Pacific Rim at 913 and Aviara Oaks Elementary at about 900. In the Encinitas Union School District (which encompasses part of Carlsbad - basically south of La Costa Ave.), there are also a few: El Camino Creek scored around 932, Mission Estancia at 919, and La Costa Heights at 903. School scores do give a good idea about academic performance, and if you are looking for a strong elementary program, I would not go below 900. Of these six schools, there should be one that you like.
Not all of the schools are compact enough so that all the kids can walk to the school, so you need to look at location of homes vs. location of the school. You might find our "Homes By School Boundary Maps" to be of interest because they allow you to compare homes while simultaneously comparing schools and scores. You'll see a link to it at http://www.EncinitasCarlsbad.com.
I hope that helps. Call if you have questions.