<?php

function my_header_image_height($height) {
return 150;
}
add filter( 'twentyeleven_header_image_height', 'my_header_image_height');

// In child themes the functions.php is applied before the parent
// theme's functions.php. So we need to wait for the parent theme to add
// it's filter before we can remove it.
add_action( 'after_setup_theme', 'my_child_theme_setup' );

function my_child_theme_setup() {
        // Removes the filter that adds the "singular" class to the body element
        // which centers the content and does not allow for a sidebar
        remove_filter( 'body_class', 'twentyeleven_body_classes' );
}

?>