select a.scanned_id
      ,stuff((select ','+b.scanned_id
               from thetable as b
              where b.scanned_id like 'A%'
                and b.scanned_order between a.scanned_order+1 and a.next_student_order-1
                for xml path('')
             ),1,1,''
            ) as answer_code
  from (select a.scanned_id
              ,a.scanned_order
              ,min(isnull(b.scanned_order,99999999)) as next_student_order
          from thetable as a
               left outer join thetable as b
                            on b.scanned_order>a.scanned_order
                           and b.scanned_id not like 'A%'
         where a.scanned_id not like 'A%'
       ) as a

;with normalized_table as 
(
	select t1.scanned_id as student, 
               t2.scanned_id as answer
 	from table_name t1 
		inner join table_name t2
		on t1.scanned_id like '1%'
		and t2.scanned_id  like 'A%'
		and t2.scanned_order > t1.scanned_order
	where not exists 
         	(select * 
	         from table_name
 	         where scanned_order between t1.scanned_order andd t2.scanned_order
	         and scanned_id like '1%')
)
select d.scanned_id, isnull(stuff(c.list,1,1,''),'') as Answer_code
from (select scanned_id 
      from table_name
      where scanned_id like '1%') d
outer apply (select ',' + t.answer
             from normalized_table t
             where t.student = d.scanned_id
             for xml path('')) c(list);