Exclude pages from wordpress 'at a glance' aka right now widget using wp_count_posts filter

functions.php

<?php
/**
* Function to retrive page id by slug
* @param string - page slug name
* @return int - page id
*/
function toddsby_get_page_by_slug($page_slug) {
	$page = get_page_by_path($page_slug);
	if ($page) {
        	return $page->ID;
	} else {
       		return null;
	}
}
/**
* Function to retrive children page id's of provided page id (workaround for missing post_parent__not_in in wp_query pre wp 3.6)
* @param int - page id
* @return array (page id and children id's)
*/
function toddsby_get_page_children_by_id($id) {
	$ids = array();
	$ids[] = $id;
	$args = array (
			'child_of' => $id
	);
	$childs = get_pages($args);
	foreach ($childs as $child) {
		$ids[] = $child->ID;
	}
	return $ids;
}
/**
* Function to filter page count on admin dashboard 'at a glance' widget
* Exclude given pages from wp_count_posts
* @param object (wordpress $counts object), string ($type of post), string ($perm not using)
* @return object $counts
*/
function toddsby_exclude_pages_from_counts( $counts,$type,$perm ) {
	if ($type != 'page') return $counts; // if $type isn't page return $counts unchanged
	$id = toddsby_get_page_by_slug('pageslug'); // get page id for page slug to exclude
	$children = toddsby_get_page_children_by_id($id); //find any children of page id
	$subtract = count($children); //count array
	$counts->publish = $counts->publish - $subtract; //subtract from publish count and store changed value
	return $counts;
}
add_filter( 'wp_count_posts', 'toddsby_exclude_pages_from_counts', 10, 3); // hook that returns 3 parameters of wp_count_post function (wp-includes/post.php)