diff --git a/backend/app/Controllers/AuthController.php b/backend/app/Controllers/AuthController.php
index b9fe4b1..017ec86 100644
--- a/backend/app/Controllers/AuthController.php
+++ b/backend/app/Controllers/AuthController.php
@@ -77,11 +77,13 @@ class AuthController
         // 2. Generate 6-digit OTP
         $otp = (string)random_int(100000, 999999);
 
-        // 3. Save OTP in Redis (TTL: 300s / 5 minutes)
+        // 3. Save OTP in Redis (TTL: 300s / 5 minutes) - Role-isolated to prevent Teacher/Student collision
         try {
             $redis = RedisClient::getInstance();
-            $otpKey = "otp:{$phoneHash}";
+            $otpKey = "otp:{$phoneHash}:{$role}";
             $redis->setex($otpKey, 300, password_hash($otp, PASSWORD_BCRYPT));
+            // Also store general key for backwards compatibility
+            $redis->setex("otp:{$phoneHash}", 300, password_hash($otp, PASSWORD_BCRYPT));
         } catch (\Exception $e) {
             error_log("Redis OTP store error: " . $e->getMessage());
         }
@@ -162,14 +164,16 @@ class AuthController
 
         $phoneHash = Security::blindIndex($cleanPhone);
 
-        // 1. Verify OTP against Redis
+        // 1. Verify OTP against Redis (Check role-isolated key first, then fallback)
         $redis = RedisClient::getInstance();
+        $otpRoleKey = "otp:{$phoneHash}:{$role}";
         $otpKey = "otp:{$phoneHash}";
-        $storedHash = $redis->get($otpKey);
+        $storedHash = $redis->get($otpRoleKey) ?: $redis->get($otpKey);
 
         $isValidOtp = false;
         if ($storedHash && password_verify($inputOtp, $storedHash)) {
             $isValidOtp = true;
+            $redis->del($otpRoleKey);
             $redis->del($otpKey); // Invalidate OTP after success
         }