This is a wild guess, because you didn’t provide (parts of) your template.
Anyway, most probably (if lessons.php is a full template) there is get_header(); somewhere at the beginning of your template file.
If you put the very code you posted in your question before this it will render, as the wp_head action is still to come.
// EDIT
My suggestion, however, is to put the function in your functions.php. Then you’d have to adapt it to your needs, of course. But this approach is much more powerful (if you need this, that is). You could do things like this:
function wpdev_156346_wp_head() {
if ( is_user_logged_in() ) {
// Some logged-in-user stuff
}
if ( is_search() ) {
// Some search-only stuff
} elseif ( is_singular() ) {
switch ( get_post_type() ) {
case 'page':
// Some page-only stuff...
break;
case 'video':
// Some video-only stuff...
break;
}
}
}
add_action( 'wp_head', 'wpdev_156346_wp_head' );