Public four-year colleges have managed to rein in the escalating cost of tuition at their institutions, according to the College Board\'s annual tuition survey, released on Tuesday. But thanks to colleges\' increasing use of merit-based aid instead of need-based aid, and the stagnating value of Pell Grants, needy students found it more difficult to finance their higher education. The survey, which the College Board presented in three reports, found that tuition at public four-year colleges rose by 7 percent in 2005-6, the smallest growth in four years, and a much lower rate than last year\'s 10 percent surge. Compared with the double-digit increases in tuition at four-year public colleges over the past couple of years, the 2005-06 increase is moderate, but at a news conference on Tuesday, College Board officials said the long-term trends in college costs were still troubling. The amount of total student aid from grants, loans, work-study arrangements, and tax benefits reached $129-billion for both undergraduate and graduate students in 2004-05, an increase of $10-billion over the previous year. After adjusting for inflation, average aid per student rose 3 percent over 2003-04, the smallest increase in the past decade.