Hi Jamal,
Does the directory "C:\student\Class_data_files" exist on your database server? If it doesn't, specify another location to store the .MDF in the Attach Databases dialog.
Database version 661 means that the database was from a SQL Server 2008 R2 instance, where version 655 means SQL Server 2008 instance. You'll need to upgrade to the R2 version in order to attach the database.