Index: wp-admin/includes/class-wp-ms-sites-list-table.php
===================================================================
--- wp-admin/includes/class-wp-ms-sites-list-table.php	(revision 21318)
+++ wp-admin/includes/class-wp-ms-sites-list-table.php	(working copy)
@@ -213,7 +213,8 @@
 				switch ( $column_name ) {
 					case 'cb': ?>
 						<th scope="row" class="check-column">
-							<input type="checkbox" id="blog_<?php echo $blog['blog_id'] ?>" name="allblogs[]" value="<?php echo esc_attr( $blog['blog_id'] ) ?>" />
+							<label class="screen-reader-text" for="blog_<?php echo $blog['blog_id']; ?>"><?php printf( __( 'Select %s' ), $blogname );
+							?></label><input type="checkbox" id="blog_<?php echo $blog['blog_id'] ?>" name="allblogs[]" value="<?php echo esc_attr( $blog['blog_id'] ) ?>" />
 						</th>
 					<?php
 					break;
Index: wp-admin/includes/class-wp-ms-users-list-table.php
===================================================================
--- wp-admin/includes/class-wp-ms-users-list-table.php	(revision 21318)
+++ wp-admin/includes/class-wp-ms-users-list-table.php	(working copy)
@@ -165,7 +165,8 @@
 				switch ( $column_name ) {
 					case 'cb': ?>
 						<th scope="row" class="check-column">
-							<input type="checkbox" id="blog_<?php echo $user->ID ?>" name="allusers[]" value="<?php echo esc_attr( $user->ID ) ?>" />
+							<label for="blog_<?php echo $user->ID; ?>" class="screen-reader-text"><?php echo sprintf( __( 'Select %s' ), $user->user_login );
+							?></label><input type="checkbox" id="blog_<?php echo $user->ID ?>" name="allusers[]" value="<?php echo esc_attr( $user->ID ) ?>" />
 						</th>
 					<?php
 					break;