sum of column returning double the value - mysql

Question

I have the following SQL query:
SELECT s.name, s.learner_tag, s.guild_id, s.id, ifnull(sum(t.xp),0) as xp, ifnull(sum(a.ap),0) as ap, (ifnull(sum(t.xp),0)/1000+ifnull(sum(a.ap),0)/100) as level, g.name
FROM student s
INNER JOIN guild g ON g.id = s.guild_id
LEFT JOIN student_task t ON s.id = t.student_id
LEFT JOIN student_achievement a ON s.id = a.student_id
WHERE s.class_id = ".$realm_id."
GROUP BY s.name, s.learner_tag, s.guild_id, s.id, g.name
ORDER BY level DESC LIMIT 10";
However the query returns double the expected value for the ap column. There is only 1 record in the student_achievement table and the value is 25. However my query returns 50 as the value of sum(a.ap). If I edit the value, it still doubles. sum(t.xp) is working fine. Can anyone spot my mistake?
Table Structure:
CREATE TABLE student
(
id INT PRIMARY KEY NOT NULL AUTO_INCREMENT,
name VARCHAR(64) NOT NULL,
guild_id INT,
class_id INT NOT NULL,
time_updated INT,
ap INT NOT NULL,
learner_tag VARCHAR(64) NOT NULL,
schoology_id INT NOT NULL,
enrollment_id INT NOT NULL,
FOREIGN KEY (guild_id) REFERENCES guild (id),
FOREIGN KEY (class_id) REFERENCES class (id)
);
CREATE TABLE student_achievement
(
id INT PRIMARY KEY NOT NULL AUTO_INCREMENT,
student_id INT NOT NULL,
achievement_id INT NOT NULL,
time_added INT,
ap INT NOT NULL,
FOREIGN KEY (student_id) REFERENCES student (id),
FOREIGN KEY (achievement_id) REFERENCES achievement (id)
);
CREATE TABLE achievement
(
id INT PRIMARY KEY NOT NULL AUTO_INCREMENT,
name VARCHAR(64) NOT NULL,
value INT NOT NULL,
repeatable TINYINT NOT NULL,
image_url VARCHAR(200) NOT NULL,
description VARCHAR(240) NOT NULL
);
CREATE TABLE task
(
id INT PRIMARY KEY NOT NULL AUTO_INCREMENT,
name VARCHAR(64) NOT NULL,
max_xp INT,
schoology_id INT,
class_id INT NOT NULL,
processed TINYINT,
type VARCHAR(15) NOT NULL,
FOREIGN KEY (class_id) REFERENCES class (id)
);