Research: This study followed a large sample of urban, racially-diverse youth from low-income families from middle school age to the beginning of high school (3.5 years on average, n=4,750) and found that kid's perceptions of parent-child communication and frequency of family dinner was positively associated. That is, the more these kids ate family dinners together, the more likely they were to view their ability to communicate with parents in a positive light.
Although the frequency of family dinners declined as the kids got older, the study suggests that teens can benefit from family dinner and that eating family dinner at middle school age has enduring positive effects, at least 2 years later. Journal of Family Psychology June 2010
Reality: The positive effects of family dinner are NOT just a middle class phenomenon. It is never too late to start family dinner, but it seems important to set a routine by the time your kids are in middle school. Teens will not be as available for family dinner, due to their independence and other time commitments, as are younger children, but having family dinner as a regular option is beneficial to them as well.