About termly boarding at public school(s), in an establishment like Eton it?s the only way that works. It has to be remembered that the pupils are not the only boarders - almost all masters including the Head and the Provost board in and around the school. Boys and masters alike come from all parts of the UK and a large number are from abroad.
On weekdays, lessons sometimes continue till late in the evening. Certain afternoons are scheduled for sports and other activities e.g. CCF on Monday afternoons and most societies meet in the night often starting at 8.30 p.m. On numerous occasions I tried ringing DS at 11p.m. without success because he was at a society meeting or other.
Saturday lessons finish at around noon and boys have sports fixtures to attend to later in the day. Some away matches can see them travelling long distances. Once I saw coaches arriving back at well past midnight from heaven knows where. On a sports free Saturday evening, it is quite usual for tutors taking their tutees to a show/play in Windsor or even London.
Even on Sundays, boys get up early to attend chapel after which they have their own free time till supper in the evening. Parents can take their child out for lunch/dinner but more often than not the child would rather the parents don?t turn up. 
Likewise, parents are welcome to watch their child play sports. I know of a rugby-mad dad who would follow his son to all rugby matches, home or away. In conclusion, there will be ample opportunities for parents to touch base with their sons even during term time and the extended term holidays more than make up for your son?s absence from home.