Perhaps not a "language lesson", but PHP has a great deployment story: upload then refresh your browser. PHP allows a strong separation between system administ

Perhaps not a "language lesson", but PHP has a great deployment story: upload then refresh your browser. PHP allows a strong separation between system administrator (who is running Apache) and the "application developers" who are people using FTP to upload their script files to a shared host. The simplicity of the system makes it easy for anyone to get started, hence the popularity. There is also the bit about taking an existing UI (written in HTML) and being able to insert programming hooks into it at will. The "minimal change" is very small, the biggest step is changing the file extension from html to php.