Cossío is born on February 22nd in Haro (La Rioja).
He finishes his BA at the Universidad de Madrid, where he meets Francisco Giner de los Ríos. He also meets Leopoldo Alas, Joaquín Costa and Marcelino Menéndez Pelayo.
He Studies Arts History at the Escuela Superior de Diplomática with Juan Facundo Riaño.
His friends from his youth are Germán Flórez, Guillem Cifre de Colonya y Alejandro Rey Colaço.
He becomes one of the first students of the Institución Libre de Enseñanza (ILE), where he will later be a teacher and remain connected until his death.
He publishes the article entitled «Carácter de la pedagogía contemporánea. El arte de saber ver» in the Boletín de la Institución Libre de Enseñanza. He moves to Bologna (Italy) alter being given a grant by the Real Colegio de San Clemente de los Españoles.
Cossío visits Italiy, Switzerland, France, the Netherlands and Belgium. He takes part in the International Conference on Education which was organized by the Belgium Ligue de l’Enseignement belga.
August- He begins a journey through Europe in order to study the organization of the Pedagogical Museums of Paris, Bern, Zurich, Munich, Vienna, Dresden, Berlin and Brussels.
He achieves after passing public examinations the post of director at the Museo Pedagógico de Instrucción Primaria (later known as Museo Pedagógico Nacional). He will remain as director of this institution until his retirement in 1929.
The ILE rents a house at 8 Paseo del Obelisco, where Giner, Cossío and Ricardo Rubio will live.
November- Giner, Azcárate and Cossío meet the philantropist from León, Villablino Francisco Fernández-Blanco y Sierra-Pambley in his birthplace in order to advise him on the creation of the Fundación Sierra-Pambley.
Cossío visits the main educational establishments in France, Belgium, Netherland and Great Britain, commissioned by the Spanish Government, together with Francisco Giner de los Ríos and a Group of teachers from the Institución Libre de Enseñanza.
He publishes his recently finished story about the Spanish painting in the Enciclopedia Popular Ilustrada de Ciencias y Artes (Madrid, Gras y Compañía).
Cossío is appointed as member of the first Patronato de la Fundación Sierra-Pambley.
The Museo Pedagógico inaugurates the first shool camps in San Vicente de la Barquera (Cantabria).
He marries (mixed marriage) Carmen López-Cortón Viqueira in Portugal.
First school camp of the ILE in Miraflores de la Sierra (Madrid).
Cossío is appointed as professor of the PhD on Superior Education at the Universidad de Madrid.
He publishes El arte en Toledo, printed in Madrid. Joaquín Sorolla paints Cossío’s first portrait, which was purchased by Archer M. Huntington for The Hispanic Society of America in New York. Three years later, the painter will make a second portrait.
He publishes the book El Greco (Madrid, Victoriano Suárez).
The German critic Julius Meier-Graefe travels to Spain and meets Cossío at the ILE. They visit Toledo together.
He visits the main educational establishments in Germany and Switzeland thanks to a grant by the Junta para Ampliación de Estudios e Investigaciones Científicas.
He takes part in the Patronato de la Casa y Museo del Greco in Toledo.
He is appointed as spokesman of the Real Patronato del Museo del Prado.
On the occasion of the 300 anniversary of the death of the Toledan painter, Cossío publishes the breif treateses Lo que se sabe de la vida del Greco (Madrid, Jiménez Fraud Editor) and El entierro del conde de Orgaz (Madrid, Jiménez Fraud Editor).
Francisco Giner de los Ríos dies on February the 18th.
Creation of the Fundación Francisco Giner de los Ríos thanks to Cossíos iniciative.
Natalia, his elder daughter, marries (civil marriage) Alberto Jiménez Fraud, director of the Residencia de Estudiantes.
Cossío is appointed as president of the Fundación Sierra-Pambley after the death of Gumersindo de Azcárate.
As the director of the Museo Pedagógico Nacional, he is appointed as the spokesperson for the Consejo de Instrucción Pública.
Visits Toledo with Albert Einstein, just as he will do with other foreign guests invited to come to Spain by the ILE.
His disciples and friends publish the book entitled De su jornada (fragmentos) (Madrid, Imprenta de Blass) on the occasion of his retirement as director at the Museo Pedagógico Nacional.
He is appointed by the Republican Government as president of the Patronato de Misiones Pedagógicas. He appears as the co director, together with Josep Piojan, of the first volume of the Summa Artis. Historia general del arte, published in Spain by Espasa-Calpe.
Julián Besteiro, president of the Republican Constituent Assembly, inaugurates Cossío’s Fountain at the mountain pass of La Morcuera( Sierra de Guadarrama), as a tribute to Cossío who had been his professor at the ILE.
Cossío becomes the first Spanish person receiving the distinction of “honorary citizen” of the Republic.
On May 15th, he atended the celebration of the third anniversary of the Teatro y Coro de Misiones Pedagógicas at Bustarviejo (Madrid).
He dies on September the 1st in Collado Mediano (Madrid) and is buried in Madrid’s civil cemetery sharing grave with Julián Sanz del Río, Fernando de Castro, Francisco Giner de los Ríos and Gumersindo de Azcárate.