The overcrowding crisis in American schools is directly attributable to high immigration:

• Without school-age immigrants and the children of immigrants, school enrollment would not have risen at all during the past decade.
  
• One in every five students has an immigrant parent. One-quarter of these children were foreign-born themselves.
  
• Immigration will account for 96 percent of the future increase in the school-age population over the next 50 years.
  
  If immigration continues at current rates, efforts to reduce class size and ease overcrowding will be doomed to failure. If immigration continues at current rates, efforts to reduce class size and ease overcrowding will be doomed to failure.
  
  The full report is available in PDF.