You can define the rules around building identifiers for students in ADAM. As a best practice, set up at the organization level as needed rather than in Client Settings.  
- Go to Rostering > Orgs.
 - Locate an org and select the Edit icon.
 - Change Restrict Identifiers for Student to On.
 - Enter the User Identifier Pattern and a Description. For example, if you want to ensure all student identifiers are 11 digits long and start with either an A or a B, the pattern definition would like this:  ^(A|B)[\d]{10}$ (details below).
 
User Identifier Pattern Details
- Use the Anchor ^ to start the string.
 - Use Quantifiers & Alternation (A|B) to specify the first character is either an A or B.
 - Use Character Class [\d]{10} to specify a total of 10 additional digits.
 - Use the Anchor $ to end the string.
 - See the tables below for more possibilities.
 
Use the online editor at https://regexr.com/ to test your rule and confirm it functions properly.
Character Classes
| . | any character except newline | 
| \w\d\s | word, digit, whitespace | 
| \W\D\S | not word, digit, whitespace | 
| [abc] | any of a, b, or c | 
| [^abc] | not a, b, or c | 
| [a-g] | character between a & g | 
Anchors
| ^abc$ | start / end of the string | 
| \b\B | word, not-word boundary | 
Escaped Characters
| \.\*\\ | escaped special characters | 
| \t\n\r | tab, linefeed, carriage return | 
Groups & Lookaround
| (abc) | capture group | 
| \1 | backreference to group #1 | 
| (?:abc) | non-capturing group | 
| (?=abc) | positive lookahead | 
| (?!abc) | negative lookahead | 
Quantifiers & Alternation
| a*a+a? | 0 or more, 1 or more, 0 or 1 | 
| a{5}a{2,} | exactly five, two or more | 
| a{1,3} | between one & three | 
| a+?a{2,}? | match as few as possible | 
| ab|cd | match ab or cd | 
Tiny Link: https://support.assessment.pearson.com/x/sAAgBg