All states that meet federal criteria will now be allowed to take part in the U.S. Department of Education's 2-year-old experiment with "growth models," which let states measure individual students' achievement gains as a way of ensuring accountability under the No Child Left Behind Act. After originally capping participation at 10 states, and approving just eight, department officials this week opened eligibility for the growth-model pilot project to all qualified states. The officials say that the first states to use those models in the project have shown it can be done without compromising the goals of the law. The new states will have to meet the same criteria as the original eight. They will have to gauge whether students are on track to attain proficiency in reading and mathematics by the end of the 2013-14 school year. They also will have to make sure their testing systems produce consistent results across grade levels. State officials will welcome the opportunity to sign up for the expanded pilot because it's clear that the NCLB law's accountability measures will eventually focus on academic growth, said Scott R. Palmer, the director of the education practice at the Washington office of the law firm Holland & Knight.