diff --git a/public/api/api_teacher_mark_lost.php b/public/api/api_teacher_mark_lost.php
new file mode 100644
index 00000000..3e636d6b
--- /dev/null
+++ b/public/api/api_teacher_mark_lost.php
@@ -0,0 +1,51 @@
+<?php
+
+/**
+ * api_teacher_mark_lost.php
+ * --------------------------------------------------------------------------
+ * Segna una prenotazione come persa o la ripristina (lostlesson Y/N).
+ * Solo staff (Admin=1 / teacher=3).
+ *
+ * Posizione: public/api/api_teacher_mark_lost.php
+ * Metodo:    POST
+ * Auth:      Bearer token (Sanctum) via _bootstrap.php
+ * Body:      booking_id=<int>&lost=<Y|N>
+ * --------------------------------------------------------------------------
+ */
+
+require_once __DIR__ . '/_bootstrap.php';
+
+// Gate staff
+$roleId = (int) $user->role_id;
+if (!in_array($roleId, [1, 3], true)) {
+    http_response_code(403);
+    echo json_encode(['success' => false, 'message' => 'Forbidden']);
+    exit;
+}
+
+$bookingId = isset($_POST['booking_id']) ? (int) $_POST['booking_id'] : 0;
+$lostRaw = isset($_POST['lost']) ? strtoupper(trim((string) $_POST['lost'])) : '';
+$lost = ($lostRaw === 'Y') ? 'Y' : 'N';
+
+if ($bookingId <= 0) {
+    http_response_code(400);
+    echo json_encode(['success' => false, 'message' => 'ID prenotazione non valido']);
+    exit;
+}
+
+try {
+    $stmt = $db->prepare(
+        "UPDATE bookingclass SET lostlesson = :lost WHERE idbookingclass = :id"
+    );
+    $stmt->execute([':lost' => $lost, ':id' => $bookingId]);
+
+    echo json_encode([
+        'success' => true,
+        'booking_id' => $bookingId,
+        'lost' => $lost,
+    ], JSON_UNESCAPED_UNICODE);
+} catch (Throwable $ex) {
+    error_log('api_teacher_mark_lost error: ' . $ex->getMessage());
+    http_response_code(500);
+    echo json_encode(['success' => false, 'message' => 'Errore aggiornamento']);
+}