diff --git a/lib/runner.rb b/lib/runner.rb
--- a/lib/runner.rb
+++ b/lib/runner.rb
@@ -25,16 +25,21 @@
     end
 
     def grade_problem(problem, options={})
-      users = User.find(:all)
-      users.each do |u|
+      User.find_each do |u|
         puts "user: #{u.login}"
         if options[:user_conditions]!=nil
           con_proc = options[:user_conditions]
           next if not con_proc.call(u)
         end
-        last_sub = Submission.find_last_by_user_and_problem(u.id,problem.id)
-        if last_sub!=nil
-          @engine.grade(last_sub)
+        if options[:all_sub]
+          Submission.where(user_id: u.id,problem_id: problem.id).find_each do |sub|
+            @engine.grade(sub)
+          end
+        else
+          last_sub = Submission.find_last_by_user_and_problem(u.id,problem.id)
+          if last_sub!=nil
+            @engine.grade(last_sub)
+          end
         end
       end
     end