best way to lock rows in MySQL?

Hi all, I'm developing an app that will enable certain users to edit records. These records will be derived from multiple tables [using joins in one to many and many to many relationships]. I would like to only have one user be able to edit *one* record at a time. This is for a teacher's grade keeping application, so I have such tables as a 'student' table, a 'score' table, 'class' table, etc [leaving out the tables relating to the joins]. So if a class is being edited, I would like to lock the particular class so that other users won't have edit privs. I do not want to lock the entire class table [nor do i want to lock the entire student table, as students in the class being edited may be in other classes that need to have grades entered]. With MySQL 3.23.22 there is no row locking - just table locking. So I'm trying to figure out the most efficiant way to 'lock' records via php4.0.2 [on linux]. Creating a locks table is one way, but I'm looking for more ideas and/or if there's something that's already proven to be very efficiant and secure. TIA, /vjl/