Hundreds of thousands of US students attend virtual public schools, but New England has been slow to adopt the high-tech model as states weigh how to manage the schools and judge their performance. There are 310,000 students in full-time public kindergarten — 12 cyberschools in 29 states across the country, but less than 800 in two New England schools, according to the nonprofit Keeping Pace. The Massachusetts Board of Elementary and Secondary Education will decide next month whether to approve TEC Connections Academy in Dedham. The state education commissioner has recommended it for approval. There is one virtual high school in New Hampshire, which has fewer than 140 students. Two virtual schools are seeking approval in Maine, but a bill in the Legislature would ban virtual charter schools there until January 2015.